Within the oil and gas industry, gauging cement quality through multiple casings and determining the status of the annuli are of paramount importance. The industry currently employs various methods verifying the hydraulic seal behind a single casing string. Typically, ultrasonic tools are run within the well to determine whether cement bonded to the outside of the casing, thereby indicating the presence of cement in the annulus between the casing and formation, or between the casing and an outer casing. Ultimately, a leak-off pressure test ensures achievement of zonal isolation. To work correctly, ultrasonic tools depend upon casing quality, the bond between the casing and the material in the annulus, and the mechanical properties of the material in the annulus. In addition, ultrasonic tools treat the material in the annulus as a single isotropic and homogenous volume, and any actual deviation from this ideal leads to measurement inaccuracies.
Current tools offer information regarding the cement bond of the innermost casing, yet fail to discriminate various depths into the cement or annular material. This leads to the possible existence of fluid migration paths at the cement-formation boundary, within the cement itself, or between the casing and an outer casing, thereby leading to a loss of zonal isolation.
No viable technologies currently allow determination of the azimuthal position of anomalies within the annular region up to the cement formation boundary to ensure no fluid-paths exist risking zonal isolation and well integrity. In addition, no viable technologies allow determination of the radial position of anomalies located within an annulus not immediately outside of the inner casing.
Prior art teaches a variety of techniques using x-rays or other radiant energy to inspect or obtain information about structures within or surrounding the borehole of a water, oil or gas well, yet none teach of a method accurately analyzing the azimuthal position of anomalies in the annular materials surrounding a wellbore in single or multi-string cased well environments. In addition, none teach of a method accurately analyzing the azimuthal position of anomalies with a means including a centralized (non-padded) tool concentric with the well casing, rather than being a padded tool requiring the source and detector assemblies contact said casing.
For example, U.S. Pat. No. 3,564,251 to Youmans teaches of using an azimuthally scanning collimated x-ray beam to produce an attenuated signal at a detector to produce a spiral-formed log of the inside of a casing or borehole surface immediately surrounding the tool, effectively embodied as an x-ray caliper. However, the reference fails to teach of a means or method to achieve such through the steel wall of single or multiple well casings, and therefore fails to discriminate between signals behind said casings and annular materials, such as cement.
U.S. Pat. No. 7,675,029 to Teague et al. teaches an apparatus measuring x-ray backscattered photons from any horizontal surface inside of a borehole referring to two-dimensional imaging techniques.
U.S. Pat. No. 7,634,059 to Wraight provides an apparatus measuring two-dimensional x-ray images of the inner surface inside of a borehole without the technical possibility of viewing the inside of the borehole in a radial direction. The reference fails, however, to teach of a means or method to achieve these images through the steel wall of single or multiple well casings, and therefore fails to discriminate between signals behind said casings and annular materials, such as cement.
U.S. Pat. No. 8,481,919 to Teague teaches of a method of producing Compton-spectrum radiation in a borehole without using radioactive isotopes, and further describes rotating collimators around a fixed source installed internally to the apparatus, but does not have solid-state detectors with collimators. It further teaches of using conical and radially symmetrical anode arrangements to permit panoramic x-ray radiation production. However, the reference fails to teach of a means or method achieving such through the steel wall of single or multiple well casings, and therefore fails to discriminate between signals behind said casings and annular materials, such as cement. The reference also fails to teach of a non-padded (i.e., concentric) tooling technique within a single or multi-string cased hole environment.
US 2013/0,009,049 by Smaardyk provides an apparatus allowing measurement of backscattered x-rays from the inner layers of a borehole. However, the reference fails to teach of a means or method achieving such through the steel wall of single or multiple well casings, and therefore fails to discriminate between signals behind said casings and annular materials, such as cement.
U.S. Pat. No. 8,138,471 to Shedlock provides a scanning-beam apparatus based on an x-ray source, a rotatable x-ray beam collimator and solid-state radiation detectors enabling the imaging of only the inner surfaces of borehole casings and pipelines. However, the reference fails to teach of a means or method achieving such through the steel wall of single or multiple well casings, and therefore fails to discriminate between signals behind said casings and annular materials, such as cement.
U.S. Pat. No. 5,326,970 to Bayless provides a tool measuring backscattered x-rays from inner surfaces of a borehole casing with a linear accelerator based x-ray source. The reference fails, however, to teach of a means or method measuring scatter through the steel wall of single or multiple well casings, and therefore fails to discriminate between the signals behind said casings and annular materials, such as cement.
U.S. Pat. No. 7,705,294 to Teague provides an apparatus measuring backscattered x-rays from the inner layers of a borehole in selected radial directions with missing segment data populated through movement of the apparatus through the borehole. The apparatus permits data generation for a two-dimensional reconstruction of the well or borehole. However, the reference teaches only of the direction, as opposed to the needed geometry, of the illuminating x-ray beams for determining the depth from which the backscattered photons originated.
U.S. Pat. No. 5,081,611 to Hornby teaches a method of back projection to determine acoustic physical parameters of the earth formation longitudinally along the borehole using a single ultrasonic transducer and a number of receivers, which are distributed along the primary axis of the tool.
U.S. Pat. No. 6,725,161 to Hillis teaches of a method of placing a transmitter in a borehole and a receiver on the surface of the earth, or a receiver in a borehole and a transmitter on the surface of the earth, with the aim to determine structural information regarding the geological materials between the transmitter and receiver.
U.S. Pat. No. 6,876,721 to Siddiqui teaches a method of correlating information taken from a core-sample with information from a borehole density log. The core-sample information derives from a CT scan of the core-sample, whereby the x-ray source and detectors are located on the outside of the sample, and therefore configured as an outside-looking-in arrangement. Various kinds of information from the CT scan such as its bulk density is compared to and correlated with the log information.
U.S. Pat. No. 4,464,569 to Flaum claims a method of determining the elemental composition of earth formations surrounding a well borehole by processing detected neutron capture gamma radiation emanating from the earth formation after neutron irradiation of the earth formation by a neutron spectroscopy logging tool.
U.S. Pat. No. 4,433,240 to Seeman presents a borehole logging tool detecting natural radiation from the rock of the formation and logs said information for representation in an intensity versus depth plot format.
U.S. Pat. No. 3,976,879 to Turcotte describes a borehole logging tool using a pulsed electromagnetic energy or photon source to detect and record the backscattered radiation from the formation surrounding the borehole, and represent that characteristic information in an intensity versus depth plot format.
U.S. Pat. No. 9,012,836 to Wilson et al. describes a method and means for creating azimuthal neutron porosity images in a wireline environment. Similar to U.S. Pat. No. 8,664,587, the reference discusses arrangement of azimuthally static detectors implemented in a wireline tool assisting an operator's interpretation of post-fracking logs by subdividing the neutron detectors into a plurality of azimuthally arranged detectors shielded within a moderator to infer directionality to incident-neutrons and gamma.
U.S. Pat. No. 4,883,956 to Manente et al. provides methods for investigating subsurface earth formations using an apparatus adapted for movement through a borehole. Depending upon the formation characteristic or characteristics to be measured, the apparatus includes a natural or artificial radiation source for irradiating the formations with penetrating radiation such as gamma rays, x-rays or neutrons. A scintillator produces light in response to detected radiation and then generates and records a signal representative of at least one characteristic of the radiation.
U.S. Pat. No. 6,078,867 to Plumb claims a method for generating a three-dimensional graphical representation of a borehole, comprising: receiving caliper data relating to the borehole, generating a three-dimensional wire mesh model of the borehole from the caliper data, and color mapping the three-dimensional wire mesh model from the caliper data based on either borehole form, rugosity and/or lithology.
U.S. Pat. No. 3,321,627 to Tittle teaches of a system of collimated detectors and collimated gamma-ray sources to determine the density of a formation outside of a borehole and represented in a density versus depth plot format. However, the reference fails to teach of a means or method achieving such through the steel wall of single or multiple well casings.